I don't believe that one can say that an attacker is "off balance" by virtue of his attack. A competent attacker can be quite balanced, in fact a good attack requires being balanced and centered.

It is, however, impossible to attack another without creating a suki or "opening". Using the principle of "irimi" we use that opening to occupy the space which the attacker wishes occupy in order to complete his attack.The action of the irimi will serve to cause the attacker to disrupt his balance.

In other words, you must take the attacker's balance. If he is competent he will not just give it to you. There is nothing inherently "off-balance" about an attack, no matter how erroneous the thinking may be behind the violent action.